Polyphenylene sulfide, or more particularly p-polyphenylene sulfide, is a highly crystalline polymeric resin with the following repeating unit: ##STR3##
Polyphenylene sulfides are typically prepared by reaction between alkali metal sulfide and dihalogenated aromatics. Polyphenylene sulfides can be used directly in the production of coatings by slurry-coating procedures; however, the principal use thereof is as a feedstock for the production of various molding-grade resins. Polyphenylene sulfides are used in injection molding, compression molding, free sintering, and coating. By far, the largest fabrication technique in the production of polyphenylene sulfide products is injection molding.
Because of their high crystalline structure, polyphenylene sulfides possess a number of excellent properties, including high resistance to wear, advantageous creep rupture properties, and high dimensional accuracy. Polyphenylene sulfide resins are particularly suitable for making components for high mechanical stress and high temperature applications.
Difficulties have been encountered in the production of moldings from polyphenylene sulfide by injection molding. These difficulties are associated with the slow mobility of the polyphenylene sulfide molecular chain, resulting in undesirably low crystallization rate and long duration of injection molding cycle. Long injection molding cycle holds up production rate and adversely affects profitability.
In order to improve the profitability of using the polyphenylene sulfide resins, it is, therefore, particularly important to improve the crystallizing characteristic, i.e., to raise the crystallizing rate, of the polyphenylene sulfide polymers. Literature surveys show that two main types of techniques have been disclosed in the prior art to improve the crystallizing rate of the polyphenylene sulfide polymers. In one type of technique, which is disclosed in Japanese Pat. App. Nos. S-63-245463, S-63-264666, P-2-182736, German Pat. No. DE-3,607,713, it was suggested adding silicon oxide, kaolin, talc, or xylene-biscarboxylic acid amide as nucleating agent to increase the crystallizing rate of polyphenylene sulfide. In another type of technique, which is disclosed in German Pat. No. DE-3,841,022, U.S. Pat. No. 5,057,264, and Japanese Pat. App. No. S-62-240359, it was suggested adding phenolic resin, polyester oligomer, or polyphenylene sulfide polymers of different molecular weight to increase the crystallization temperature thereof.
Because of its unique combination of properties, polyphenylene sulfide is finding increased demands and applications, particularly in the electrical and electronic industries. Although improvements have been made regarding the fabricability thereof, mainly to reduce the duration of the injection molding cycle, additional efforts are still required to further increase the crystallizing rate of polyphenylene sulfide to thus bring the cost of polyphenylene sulfide products to a more acceptable level.